Implement TokenFilter and refactor Pl_QPDFTokenizer

Implement a TokenFilter class and refactor Pl_QPDFTokenizer to use a TokenFilter class called ContentNormalizer. Pl_QPDFTokenizer is now a general filter that passes data through a TokenFilter.

Implement TokenFilter and refactor Pl_QPDFTokenizer
Implement a TokenFilter class and refactor Pl_QPDFTokenizer to use a TokenFilter class called ContentNormalizer. Pl_QPDFTokenizer is now a general filter that passes data through a TokenFilter.
Jay Berkenbilt
1 parent b8723e97
Showing 16 changed files with 631 additions and 115 deletions
ChangeLog
include/qpdf/QPDFObjectHandle.hh
include/qpdf/QPDFTokenizer.hh
libqpdf/ContentNormalizer.cc
libqpdf/Pl_QPDFTokenizer.cc
libqpdf/QPDFObjectHandle.cc
libqpdf/QPDFTokenizer.cc
libqpdf/QPDFWriter.cc
libqpdf/QPDF_Stream.cc
libqpdf/build.mk
libqpdf/qpdf/ContentNormalizer.hh
libqpdf/qpdf/Pl_QPDFTokenizer.hh
libqpdf/qpdf/QPDF_Stream.hh
qpdf/qtest/qpdf.test
qpdf/qtest/qpdf/token-filters-out.pdf
qpdf/test_driver.cc
@@ -107,6 +107,49 @@
 	applications that use page-level APIs in QPDFObjectHandle to be
 	more tolerant of certain types of damaged files.
+	* Add QPDFObjectHandle::TokenFilter class and methods to use it to
+	perform lexical filtering on content streams. You can call
+	QPDFObjectHandle::addTokenFilter on stream object, or you can call
+	the higher level QPDFObjectHandle::addContentTokenFilter on a page
+	object to cause the stream's contents to passed through a token
+	filter while being retrieved by QPDFWriter or any other consumer.
+	For details on using TokenFilter, please see comments in
+	QPDFObjectHandle.hh.
+
+	* Enhance the string, type QPDFTokenizer::Token constructor to
+	initialize a raw value in addition to a value. Tokens have a
+	value, which is a canonical representation, and a raw value. For
+	all tokens except strings and names, the raw value and the value
+	are the same. For strings, the value excludes the outer delimiters
+	and has non-printing characters normalized. For names, the value
+	resolves non-printing characters. In order to better facilitate
+	token filters that mostly preserve contents and to enable
+	developers to be mostly unconcerned about the nuances of token
+	values and raw values, creating string and name tokens now
+	properly handles this subtlety of values and raw values. When
+	constructing string tokens, take care to avoid passing in the
+	outer delimiters. This has always been the case, but it is now
+	clarified in comments in QPDFObjectHandle.hh::TokenFilter. This
+	has no impact on any existing code unless there's some code
+	somewhere that was relying on Token::getRawValue() returning an
+	empty string for a manually constructed token. The token class's
+	operator== method still only looks at type and value, not raw
+	value. For example, string tokens for <41> and (A) would still be
+	equal because both are representations of the string "A".
+
+	* Add QPDFObjectHandle::isDataModified method. This method just
+	returns true if addTokenFilter has been called on the stream. It
+	enables a caller to determine whether it is safe to optimize away
+	piping of stream data in cases where the input and output are
+	expected to be the same. QPDFWriter uses this internally to skip
+	the optimization of not re-compressing already compressed streams
+	if addTokenFilter has been called. Most developers will not have
+	to worry about this as it is used internally in the library in the
+	places that need it. If you are manually retrieving stream data
+	with QPDFObjectHandle::getStreamData or
+	QPDFObjectHandle::pipeStreamData, you don't need to worry about
+	this at all.
+
 2018-02-04  Jay Berkenbilt  <ejb@ql.org>
 	* Add QPDFWriter::setLinearizationPass1Filename method and
@@ -35,6 +35,7 @@
 #include <qpdf/PointerHolder.hh>
 #include <qpdf/Buffer.hh>
 #include <qpdf/InputSource.hh>
+#include <qpdf/QPDFTokenizer.hh>
 #include <qpdf/QPDFObject.hh>
@@ -76,6 +77,66 @@ class QPDFObjectHandle
 				       Pipeline* pipeline) = 0;
     };
+    // The TokenFilter class provides a way to filter content streams
+    // in a lexically aware fashion. TokenFilters can be attached to
+    // streams using the addTokenFilter or addContentTokenFilter
+    // methods. The handleToken method is called for each token,
+    // including the eof token, and then handleEOF is called at the
+    // very end. Handlers may call write (or writeToken) to pass data
+    // downstream. The finish() method must be called exactly one time
+    // to ensure that any written data is flushed out. The default
+    // handleEOF calls finish. If you override handleEOF, you must
+    // ensure that finish() is called either there or in response to
+    // whatever event causes you to terminate creation of output.
+    // Failure to call finish() may result in some of the data you
+    // have written being lost. You should not rely on a destructor
+    // for calling finish() since the destructor call may occur later
+    // than you expect. Please see examples/token-filters.cc for
+    // examples of using TokenFilters.
+    //
+    // Please note that when you call token.getValue() on a token of
+    // type tt_string, you get the string value without any
+    // delimiters. token.getRawValue() will return something suitable
+    // for being written to output, or calling writeToken with a
+    // string token will also work. The correct way to construct a
+    // string token that would write the literal value (str) is
+    // QPDFTokenizer::Token(QPDFTokenizer::tt_string, "str").
+    class TokenFilter
+    {
+      public:
+        QPDF_DLL
+        TokenFilter()
+        {
+        }
+        QPDF_DLL
+        virtual ~TokenFilter()
+        {
+        }
+        virtual void handleToken(QPDFTokenizer::Token const&) = 0;
+        virtual void handleEOF()
+        {
+            // If you override handleEOF, you must be sure to call
+            // finish().
+            finish();
+        }
+
+        // This is called internally by the qpdf library.
+        void setPipeline(Pipeline*);
+
+      protected:
+        QPDF_DLL
+        void write(char const* data, size_t len);
+        QPDF_DLL
+        void write(std::string const& str);
+        QPDF_DLL
+        void writeToken(QPDFTokenizer::Token const&);
+        QPDF_DLL
+        void finish();
+
+      private:
+        Pipeline* pipeline;
+    };
+
     // This class is used by parse to decrypt strings when reading an
     // object that contains encrypted strings.
     class StringDecrypter
@@ -223,6 +284,23 @@ class QPDFObjectHandle
     static void parseContentStream(QPDFObjectHandle stream_or_array,
                                    ParserCallbacks* callbacks);
+    // Attach a token filter to a page's contents. If the page's
+    // contents is an array of streams, it is automatically coalesced.
+    // The token filter is applied to the page's contents as a single
+    // stream.
+    QPDF_DLL
+    void addContentTokenFilter(PointerHolder<TokenFilter> token_filter);
+
+    // As of qpdf 8, it is possible to add custom token filters to a
+    // stream. The tokenized stream data is passed through the token
+    // filter after all original filters but before content stream
+    // normalization if requested. This is a low-level interface to
+    // add it to a stream. You will usually want to call
+    // addContentTokenFilter instead, which can be applied to a page
+    // object, and which will automatically handle the case of pages
+    // whose contents are split across multiple streams.
+    void addTokenFilter(PointerHolder<TokenFilter> token_filter);
+
     // Type-specific factories
     QPDF_DLL
     static QPDFObjectHandle newNull();
@@ -414,6 +492,13 @@ class QPDFObjectHandle
     QPDF_DLL
     QPDFObjectHandle getDict();
+    // If addTokenFilter has been called for this stream, then the
+    // original data should be considered to be modified. This means we
+    // should avoid optimizations such as not filtering a stream that
+    // is already compressed.
+    QPDF_DLL
+    bool isDataModified();
+
     // Returns filtered (uncompressed) stream data.  Throws an
     // exception if the stream is filtered and we can't decode it.
     QPDF_DLL
@@ -608,7 +693,7 @@ class QPDFObjectHandle
     // stream or an array of streams. If this page's content is an
     // array, concatenate the streams into a single stream. This can
     // be useful when working with files that split content streams in
-    // arbitary spots, such as in the middle of a token, as that can
+    // arbitrary spots, such as in the middle of a token, as that can
     // confuse some software. You could also call this after calling
     // addPageContents.
     QPDF_DLL
@@ -62,13 +62,8 @@ class QPDFTokenizer
     {
       public:
 	Token() : type(tt_bad) {}
-
-	Token(token_type_e type, std::string const& value) :
-	    type(type),
-	    value(value)
-	{
-	}
-
+        QPDF_DLL
+	Token(token_type_e type, std::string const& value);
 	Token(token_type_e type, std::string const& value,
 	      std::string raw_value, std::string error_message) :
 	    type(type),
@@ -93,7 +88,7 @@ class QPDFTokenizer
 	{
 	    return this->error_message;
 	}
-	bool operator==(Token const& rhs)
+	bool operator==(Token const& rhs) const
 	{
 	    // Ignore fields other than type and value
 	    return ((this->type != tt_bad) &&
+#include <qpdf/ContentNormalizer.hh>
+#include <qpdf/QUtil.hh>
+
+ContentNormalizer::ContentNormalizer()
+{
+}
+
+ContentNormalizer::~ContentNormalizer()
+{
+}
+
+void
+ContentNormalizer::handleToken(QPDFTokenizer::Token const& token)
+{
+    std::string value = token.getRawValue();
+    QPDFTokenizer::token_type_e token_type = token.getType();
+
+    switch (token_type)
+    {
+      case QPDFTokenizer::tt_space:
+        {
+            size_t len = value.length();
+            for (size_t i = 0; i < len; ++i)
+            {
+                char ch = value.at(i);
+                if (ch == '\r')
+                {
+                    if ((i + 1 < len) && (value.at(i + 1) == '\n'))
+                    {
+                        // ignore
+                    }
+                    else
+                    {
+                        write("\n");
+                    }
+                }
+                else
+                {
+                    write(&ch, 1);
+                }
+            }
+        }
+        break;
+
+      case QPDFTokenizer::tt_string:
+        // Replacing string and name tokens in this way normalizes
+        // their representation as this will automatically handle
+        // quoting of unprintable characters, etc.
+        writeToken(QPDFTokenizer::Token(
+                       QPDFTokenizer::tt_string, token.getValue()));
+	break;
+
+      case QPDFTokenizer::tt_name:
+        writeToken(QPDFTokenizer::Token(
+                       QPDFTokenizer::tt_name, token.getValue()));
+	break;
+
+      default:
+        writeToken(token);
+	break;
+    }
+
+    value = token.getRawValue();
+    if (((token_type == QPDFTokenizer::tt_string) ||
+         (token_type == QPDFTokenizer::tt_name)) &&
+        ((value.find('\r') != std::string::npos) ||
+         (value.find('\n') != std::string::npos)))
+    {
+        write("\n");
+    }
+}
+
+void
+ContentNormalizer::handleEOF()
+{
+    finish();
+}
 #include <qpdf/Pl_QPDFTokenizer.hh>
-#include <qpdf/QPDF_String.hh>
-#include <qpdf/QPDF_Name.hh>
 #include <qpdf/QTC.hh>
-#include <qpdf/QUtil.hh>
 #include <stdexcept>
 #include <string.h>
-Pl_QPDFTokenizer::Pl_QPDFTokenizer(char const* identifier, Pipeline* next) :
-    Pipeline(identifier, next),
-    just_wrote_nl(false),
+Pl_QPDFTokenizer::Members::Members() :
+    filter(0),
     last_char_was_cr(false),
     unread_char(false),
     char_to_unread('\0')
 {
-    tokenizer.allowEOF();
-    tokenizer.includeIgnorable();
 }
-Pl_QPDFTokenizer::~Pl_QPDFTokenizer()
+Pl_QPDFTokenizer::Members::~Members()
 {
 }
-void
-Pl_QPDFTokenizer::writeNext(char const* buf, size_t len)
+Pl_QPDFTokenizer::Pl_QPDFTokenizer(
+    char const* identifier,
+    QPDFObjectHandle::TokenFilter* filter)
+    :
+    Pipeline(identifier, 0),
+    m(new Members)
 {
-    if (len)
-    {
-	getNext()->write(QUtil::unsigned_char_pointer(buf), len);
-	this->just_wrote_nl = (buf[len-1] == '\n');
-    }
+    m->filter = filter;
+    m->tokenizer.allowEOF();
+    m->tokenizer.includeIgnorable();
 }
-void
-Pl_QPDFTokenizer::writeToken(QPDFTokenizer::Token& token)
+Pl_QPDFTokenizer::~Pl_QPDFTokenizer()
 {
-    std::string value = token.getRawValue();
-
-    switch (token.getType())
-    {
-      case QPDFTokenizer::tt_space:
-        {
-            size_t len = value.length();
-            for (size_t i = 0; i < len; ++i)
-            {
-                char ch = value.at(i);
-                if (ch == '\r')
-                {
-                    if ((i + 1 < len) && (value.at(i + 1) == '\n'))
-                    {
-                        // ignore
-                    }
-                    else
-                    {
-                        writeNext("\n", 1);
-                    }
-                }
-                else
-                {
-                    writeNext(&ch, 1);
-                }
-            }
-        }
-        value.clear();
-        break;
-
-      case QPDFTokenizer::tt_string:
-	value = QPDF_String(token.getValue()).unparse();
-
-	break;
-
-      case QPDFTokenizer::tt_name:
-	value = QPDF_Name(token.getValue()).unparse();
-	break;
-
-      default:
-	break;
-    }
-    writeNext(value.c_str(), value.length());
 }
 void
 Pl_QPDFTokenizer::processChar(char ch)
 {
-    tokenizer.presentCharacter(ch);
+    this->m->tokenizer.presentCharacter(ch);
     QPDFTokenizer::Token token;
-    if (tokenizer.getToken(token, this->unread_char, this->char_to_unread))
+    if (this->m->tokenizer.getToken(
+            token, this->m->unread_char, this->m->char_to_unread))
     {
-	writeToken(token);
-        std::string value = token.getRawValue();
-        QPDFTokenizer::token_type_e token_type = token.getType();
-        if (((token_type == QPDFTokenizer::tt_string) ||
-             (token_type == QPDFTokenizer::tt_name)) &&
-            ((value.find('\r') != std::string::npos) ||
-             (value.find('\n') != std::string::npos)))
+	this->m->filter->handleToken(token);
+        if ((token.getType() == QPDFTokenizer::tt_word) &&
+            (token.getValue() == "ID"))
         {
-	    writeNext("\n", 1);
-	}
-	if ((token.getType() == QPDFTokenizer::tt_word) &&
-	    (token.getValue() == "ID"))
-	{
             QTC::TC("qpdf", "Pl_QPDFTokenizer found ID");
-            tokenizer.expectInlineImage();
-	}
+            this->m->tokenizer.expectInlineImage();
+        }
     }
 }
@@ -109,10 +53,10 @@ Pl_QPDFTokenizer::processChar(char ch)
 void
 Pl_QPDFTokenizer::checkUnread()
 {
-    if (this->unread_char)
+    if (this->m->unread_char)
     {
-	processChar(this->char_to_unread);
-	if (this->unread_char)
+	processChar(this->m->char_to_unread);
+	if (this->m->unread_char)
 	{
 	    throw std::logic_error(
 		"INTERNAL ERROR: unread_char still true after processing "
@@ -135,20 +79,13 @@ Pl_QPDFTokenizer::write(unsigned char* buf, size_t len)
 void
 Pl_QPDFTokenizer::finish()
 {
-    this->tokenizer.presentEOF();
+    this->m->tokenizer.presentEOF();
     QPDFTokenizer::Token token;
-    if (tokenizer.getToken(token, this->unread_char, this->char_to_unread))
+    if (this->m->tokenizer.getToken(
+            token, this->m->unread_char, this->m->char_to_unread))
     {
-        writeToken(token);
-        if (unread_char)
-        {
-            if (this->char_to_unread == '\r')
-            {
-                this->char_to_unread = '\n';
-            }
-            writeNext(&this->char_to_unread, 1);
-        }
+	this->m->filter->handleToken(token);
     }
-    getNext()->finish();
+    this->m->filter->handleEOF();
 }
@@ -63,6 +63,50 @@ CoalesceProvider::provideStreamData(int, int, Pipeline* p)
 }
 void
+QPDFObjectHandle::TokenFilter::setPipeline(Pipeline* p)
+{
+    this->pipeline = p;
+}
+
+void
+QPDFObjectHandle::TokenFilter::write(char const* data, size_t len)
+{
+    if (! this->pipeline)
+    {
+        throw std::logic_error(
+            "TokenFilter::write called before setPipeline");
+    }
+    if (len)
+    {
+	this->pipeline->write(QUtil::unsigned_char_pointer(data), len);
+    }
+}
+
+void
+QPDFObjectHandle::TokenFilter::write(std::string const& str)
+{
+    write(str.c_str(), str.length());
+}
+
+void
+QPDFObjectHandle::TokenFilter::writeToken(QPDFTokenizer::Token const& token)
+{
+    std::string value = token.getRawValue();
+    write(value.c_str(), value.length());
+}
+
+void
+QPDFObjectHandle::TokenFilter::finish()
+{
+    if (! this->pipeline)
+    {
+        throw std::logic_error(
+            "TokenFilter::finish called before setPipeline");
+    }
+    this->pipeline->finish();
+}
+
+void
 QPDFObjectHandle::ParserCallbacks::terminateParsing()
 {
     throw TerminateParsing();
@@ -508,6 +552,13 @@ QPDFObjectHandle::getDict()
     return dynamic_cast<QPDF_Stream*>(obj.getPointer())->getDict();
 }
+bool
+QPDFObjectHandle::isDataModified()
+{
+    assertStream();
+    return dynamic_cast<QPDF_Stream*>(obj.getPointer())->isDataModified();
+}
+
 void
 QPDFObjectHandle::replaceDict(QPDFObjectHandle new_dict)
 {
@@ -1033,6 +1084,21 @@ QPDFObjectHandle::parseContentStream_data(
     }
 }
+void
+QPDFObjectHandle::addContentTokenFilter(PointerHolder<TokenFilter> filter)
+{
+    coalesceContentStreams();
+    this->getKey("/Contents").addTokenFilter(filter);
+}
+
+void
+QPDFObjectHandle::addTokenFilter(PointerHolder<TokenFilter> filter)
+{
+    assertStream();
+    return dynamic_cast<QPDF_Stream*>(
+        obj.getPointer())->addTokenFilter(filter);
+}
+
 QPDFObjectHandle
 QPDFObjectHandle::parse(PointerHolder<InputSource> input,
                         std::string const& object_description,
@@ -7,6 +7,7 @@
 #include <qpdf/QTC.hh>
 #include <qpdf/QPDFExc.hh>
 #include <qpdf/QUtil.hh>
+#include <qpdf/QPDFObjectHandle.hh>
 #include <stdexcept>
 #include <string.h>
@@ -39,6 +40,23 @@ QPDFTokenizer::Members::~Members()
 {
 }
+QPDFTokenizer::Token::Token(token_type_e type, std::string const& value) :
+    type(type),
+    value(value),
+    raw_value(value)
+{
+    if (type == tt_string)
+    {
+        raw_value = QPDFObjectHandle::newString(value).unparse();
+    }
+    else if (type == tt_string)
+    {
+        raw_value = QPDFObjectHandle::newName(value).unparse();
+    }
+}
+
+
+
 QPDFTokenizer::QPDFTokenizer() :
     m(new Members())
 {
@@ -1591,7 +1591,8 @@ QPDFWriter::unparseObject(QPDFObjectHandle object, int level,
 	{
 	    is_metadata = true;
 	}
-	bool filter = (this->m->compress_streams ||
+	bool filter = (object.isDataModified() ||
+                       this->m->compress_streams ||
                        this->m->stream_decode_level);
 	if (this->m->compress_streams)
 	{
@@ -1602,7 +1603,8 @@ QPDFWriter::unparseObject(QPDFObjectHandle object, int level,
 	    // compressed with a lossy compression scheme, but we
 	    // don't support any of those right now.
 	    QPDFObjectHandle filter_obj = stream_dict.getKey("/Filter");
-	    if (filter_obj.isName() &&
+            if ((! object.isDataModified()) &&
+                filter_obj.isName() &&
 		((filter_obj.getName() == "/FlateDecode") ||
 		 (filter_obj.getName() == "/Fl")))
 	    {
@@ -13,7 +13,7 @@
 #include <qpdf/Pl_RunLength.hh>
 #include <qpdf/Pl_DCT.hh>
 #include <qpdf/Pl_Count.hh>
-
+#include <qpdf/ContentNormalizer.hh>
 #include <qpdf/QTC.hh>
 #include <qpdf/QPDF.hh>
 #include <qpdf/QPDFExc.hh>
@@ -91,6 +91,12 @@ QPDF_Stream::getDict() const
     return this->stream_dict;
 }
+bool
+QPDF_Stream::isDataModified() const
+{
+    return (! this->token_filters.empty());
+}
+
 PointerHolder<Buffer>
 QPDF_Stream::getStreamData(qpdf_stream_decode_level_e decode_level)
 {
@@ -440,21 +446,36 @@ QPDF_Stream::pipeStreamData(Pipeline* pipeline,
     // create to be deleted when this function finishes.
     std::vector<PointerHolder<Pipeline> > to_delete;
+    PointerHolder<ContentNormalizer> normalizer;
     if (filter)
     {
 	if (encode_flags & qpdf_ef_compress)
 	{
-	    pipeline = new Pl_Flate("compress object stream", pipeline,
+	    pipeline = new Pl_Flate("compress stream", pipeline,
 				    Pl_Flate::a_deflate);
 	    to_delete.push_back(pipeline);
 	}
 	if (encode_flags & qpdf_ef_normalize)
 	{
-	    pipeline = new Pl_QPDFTokenizer("normalizer", pipeline);
+            normalizer = new ContentNormalizer();
+            normalizer->setPipeline(pipeline);
+	    pipeline = new Pl_QPDFTokenizer(
+                "normalizer", normalizer.getPointer());
 	    to_delete.push_back(pipeline);
 	}
+        for (std::vector<PointerHolder<
+                 QPDFObjectHandle::TokenFilter> >::reverse_iterator iter =
+                 this->token_filters.rbegin();
+             iter != this->token_filters.rend(); ++iter)
+        {
+            (*iter)->setPipeline(pipeline);
+            pipeline = new Pl_QPDFTokenizer(
+                "token filter", (*iter).getPointer());
+            to_delete.push_back(pipeline);
+        }
+
 	for (std::vector<std::string>::reverse_iterator iter = filters.rbegin();
 	     iter != filters.rend(); ++iter)
 	{
@@ -613,6 +634,13 @@ QPDF_Stream::replaceStreamData(
 }
 void
+QPDF_Stream::addTokenFilter(
+    PointerHolder<QPDFObjectHandle::TokenFilter> token_filter)
+{
+    this->token_filters.push_back(token_filter);
+}
+
+void
 QPDF_Stream::replaceFilterData(QPDFObjectHandle const& filter,
 			       QPDFObjectHandle const& decode_parms,
 			       size_t length)
@@ -9,6 +9,7 @@ SRCS_libqpdf = \
 	libqpdf/BitWriter.cc \
 	libqpdf/Buffer.cc \
 	libqpdf/BufferInputSource.cc \
+	libqpdf/ContentNormalizer.cc \
 	libqpdf/FileInputSource.cc \
 	libqpdf/InputSource.cc \
 	libqpdf/InsecureRandomDataProvider.cc \
+#ifndef __CONTENTNORMALIZER_HH__
+#define __CONTENTNORMALIZER_HH__
+
+#include <qpdf/QPDFObjectHandle.hh>
+
+class ContentNormalizer: public QPDFObjectHandle::TokenFilter
+{
+  public:
+    ContentNormalizer();
+    virtual ~ContentNormalizer();
+    virtual void handleToken(QPDFTokenizer::Token const&);
+    virtual void handleEOF();
+};
+
+#endif // __CONTENTNORMALIZER_HH__
@@ -4,6 +4,8 @@
 #include <qpdf/Pipeline.hh>
 #include <qpdf/QPDFTokenizer.hh>
+#include <qpdf/PointerHolder.hh>
+#include <qpdf/QPDFObjectHandle.hh>
 //
 // Treat incoming text as a stream consisting of valid PDF tokens, but
@@ -16,7 +18,8 @@
 class Pl_QPDFTokenizer: public Pipeline
 {
   public:
-    Pl_QPDFTokenizer(char const* identifier, Pipeline* next);
+    Pl_QPDFTokenizer(char const* identifier,
+                     QPDFObjectHandle::TokenFilter* filter);
     virtual ~Pl_QPDFTokenizer();
     virtual void write(unsigned char* buf, size_t len);
     virtual void finish();
@@ -24,14 +27,25 @@ class Pl_QPDFTokenizer: public Pipeline
   private:
     void processChar(char ch);
     void checkUnread();
-    void writeNext(char const*, size_t len);
-    void writeToken(QPDFTokenizer::Token&);
-
-    QPDFTokenizer tokenizer;
-    bool just_wrote_nl;
-    bool last_char_was_cr;
-    bool unread_char;
-    char char_to_unread;
+
+    class Members
+    {
+        friend class Pl_QPDFTokenizer;
+
+      public:
+        ~Members();
+
+      private:
+        Members();
+        Members(Members const&);
+
+        QPDFObjectHandle::TokenFilter* filter;
+        QPDFTokenizer tokenizer;
+        bool last_char_was_cr;
+        bool unread_char;
+        char char_to_unread;
+    };
+    PointerHolder<Members> m;
 };
 #endif // __PL_QPDFTOKENIZER_HH__
@@ -20,6 +20,7 @@ class QPDF_Stream: public QPDFObject
     virtual QPDFObject::object_type_e getTypeCode() const;
     virtual char const* getTypeName() const;
     QPDFObjectHandle getDict() const;
+    bool isDataModified() const;
     // See comments in QPDFObjectHandle.hh for these methods.
     bool pipeStreamData(Pipeline*,
@@ -35,6 +36,8 @@ class QPDF_Stream: public QPDFObject
 	PointerHolder<QPDFObjectHandle::StreamDataProvider> provider,
 	QPDFObjectHandle const& filter,
 	QPDFObjectHandle const& decode_parms);
+    void addTokenFilter(
+        PointerHolder<QPDFObjectHandle::TokenFilter> token_filter);
     void replaceDict(QPDFObjectHandle new_dict);
@@ -72,6 +75,8 @@ class QPDF_Stream: public QPDFObject
     size_t length;
     PointerHolder<Buffer> stream_data;
     PointerHolder<QPDFObjectHandle::StreamDataProvider> stream_provider;
+    std::vector<
+        PointerHolder<QPDFObjectHandle::TokenFilter> > token_filters;
 };
 #endif // __QPDF_STREAM_HH__
@@ -758,6 +758,19 @@ $td-&gt;runtest(&quot;check output&quot;,
 show_ntests();
 # ----------
+$td->notify("--- Token filters ---");
+$n_tests += 2;
+
+$td->runtest("token filter",
+             {$td->COMMAND => "test_driver 41 coalesce.pdf"},
+             {$td->STRING => "test 41 done\n", $td->EXIT_STATUS => 0},
+             $td->NORMALIZE_NEWLINES);
+$td->runtest("check output",
+             {$td->FILE => "a.pdf"},
+             {$td->FILE => "token-filters-out.pdf"});
+
+show_ntests();
+# ----------
 $td->notify("--- Newline before endstream ---");
 $n_tests += 10;
@@ -97,6 +97,36 @@ ParserCallbacks::handleEOF()
     std::cout << "-EOF-" << std::endl;
 }
+class TokenFilter: public QPDFObjectHandle::TokenFilter
+{
+  public:
+    TokenFilter()
+    {
+    }
+    virtual ~TokenFilter()
+    {
+    }
+    virtual void handleToken(QPDFTokenizer::Token const& t)
+    {
+        if (t == QPDFTokenizer::Token(QPDFTokenizer::tt_string, "Potato"))
+        {
+            // Exercise unparsing of strings by token constructor
+            writeToken(
+                QPDFTokenizer::Token(QPDFTokenizer::tt_string, "Salad"));
+        }
+        else
+        {
+            writeToken(t);
+        }
+    }
+    virtual void handleEOF()
+    {
+        writeToken(QPDFTokenizer::Token(QPDFTokenizer::tt_name, "/bye"));
+        write("\n");
+        finish();
+    }
+};
+
 static std::string getPageContents(QPDFObjectHandle page)
 {
     PointerHolder<Buffer> b1 =
@@ -1345,6 +1375,22 @@ void runtest(int n, char const* filename1, char const* arg2)
         w.setStaticID(true);
         w.write();
     }
+    else if (n == 41)
+    {
+        // Apply a token filter. This test case is crafted to work
+        // with coalesce.pdf.
+        std::vector<QPDFObjectHandle> pages = pdf.getAllPages();
+        for (std::vector<QPDFObjectHandle>::iterator iter =
+                 pages.begin();
+             iter != pages.end(); ++iter)
+        {
+            (*iter).addContentTokenFilter(new TokenFilter);
+        }
+        QPDFWriter w(pdf, "a.pdf");
+	w.setQDFMode(true);
+        w.setStaticID(true);
+        w.write();
+    }
     else
     {
 	throw std::runtime_error(std::string("invalid test ") +